Beryllium is a metal that is used in a wide variety of industries including electronics, aerospace, defense, and the Department of Energy (DOE) complexes. Exposure to beryllium containing particles can lead to a lung disease called Chronic Beryllium Disease (CBD). CBD involves an uncontrolled immune response in the lungs that can lead to deterioration in breathing capacity and ultimately death. It is clear that even in processes where beryllium dust has been controlled to very low levels, cases of disease still persist. In fact, there have been cases of CBD reported in people that have had no obvious direct contact with beryllium operations. Despite the fact that very low exposure levels can lead to CBD, the onset of disease can take decades.
Recent new regulations from DOE dictate a permissible exposure limit of 0.2 μg/m3 in air, a housekeeping level of 3 μg/100 cm2 on a surface, and a release level for materials after beryllium exposure where the surface contamination due to beryllium must not exceed 0.2 μg/100 cm2. The present technique for detecting beryllium is a surface analysis that involves wiping an area with a filter paper, performing a microwave digestion with acid to dissolute beryllium or its compounds, and then analyze by inductively coupled plasma (ICP) atomic emission spectroscopy (AES). For analyzing airborne samples, one draws a known quantity of air through a filtering medium and then it is treated in a similar fashion to the surface wipes. There is a discussion in the beryllium community if the permissible air exposure limit needs to be lowered to 0.02 μg/m3. For air sampling one cubic meter of air through the filters is typically passed in eight hours, there are also forthcoming regulations where the filters would be analyzed over shorter periods (short term exposure limits or STEL) such as 15 minutes to ensure that the rate 0.2 μg/m3 is not exceeded in any 15 minute interval during the eight hour period, this would require one to measure beryllium after only 15 minutes of exposure and down to 0.0008 μg on these filters. Currently, thousands of surface wipes and air filters are analyzed annually for beryllium. Similarly OSHA has been contemplating reducing air exposure limit from 2 μg/m3 to a much lower value. In addition OSHA has detected airborne levels of beryllium at numerous sites within the United States. The ICP-AES technique requires highly trained operators and the entire sample is consumed in order to meet the detection levels so that a sample that is identified as positive for beryllium cannot be checked or verified with a second run. Optical fluorescence methods such as ASTM D7202 and ASTM D7854 and other equivalent methods (e.g., NIOSH analytical methods 7704 and 9110) remove these drawbacks and may be automated to increase throughput and decrease labor requirements. The standard fluorescence methods being currently used may be easily changed for use with present invention.
There are several publications of being able to quantitatively detect beryllium with a fluorescent indicator (Matsumiya et al 2001 or Matsumiya, Minogue et al 2005, Agrawal et al 2006, Ashley et al 2007, Agrawal et al 2008 and Agrawal et al 2011, and U.S. Pat. Nos. 7,129,093; 8,450,117; 8,945,931, and published patent application US 20110092377). All of these publications and their teachings are incorporated herein by reference.
Matsumiya teaches the use of a fluorescent dye, 10-hydroxybenzo[h]quinoline-7-sulfonate (HBQS). The HBQS dye selectively binds to beryllium and results in high fluorescence intensity at high pH. FIG. 1 has been reproduced from Matsumiya where the fluorescence intensity is shown as a function of pH when an excitation wavelength of 384 nm was used and the emission was measured at 478 nm. This clearly shows a strong dependence on pH where the maximum intensity is in the region of about 12, and a preferred range of measurement is 12 to about 12.85 with a sharp drop off after that. Thus in order to be able to detect low values of beryllium in samples by this method, an effort was made (see U.S. Pat. No. 7,129,093) to improve the dye solutions so that when sample solutions (typically acidic solutions) are mixed with dye solutions one obtains a pH in this range without having to rely on titrating back to a pH of 12 as done by Matsumiya. Another advantage of high pH of this mixture is that this solution is not able to support solubility of most metals in solution at these pH's, which precipitate out and reduce chances of interference that could have been caused by their presence. U.S. Pat. No. 7,129,093 modified Matsumiya's dye solution by adding a pH buffer (or buffer) so that when the dye solution was mixed with the acidic solution containing beryllium in a ratio of 19:1 (called 20× dilution), then the pH was maintained in the range of about 12 to 12.85 without having to titrate this mixture. Dilution ratio of 20× implies that the sample (or beryllium containing) solution has been diluted 20 times by adding the dye solution in the above volumetric ratio; similarly a dilution ratio of 5× will imply that the sample (or beryllium containing) solution has been diluted 5 times by adding the dye solution—i.e., one part by volume of the sample solution is mixed with 4 parts of the dye solution by volume and so on for other dilution ratios. However, it was important to start with a pH of about 12.85 of the buffered dye solution so that when it was mixed with the acidic samples in a dilution ratio of 20× one obtained the pH of the mixture in the range of about 12 to 12.85. This allowed simplifying Matsumiya's method since no titration was needed to maintain the pH of this mixture as long as it was in the desired pH range. In addition one did not have to worry about accounting for dilution effects caused by titration due to adding of differential volumes of the base to the solution being analyzed to bring the pH in the desired range.
U.S. Pat. Nos. 8,450,117 and 8,945,931, furthered the system where principally the dye solution described in U.S. Pat. No. 7,129,093 was used, but enhanced the sample preparation by teaching superior methods of dissolving refractory compounds of beryllium (such as high fired beryllium oxide), and increasing the method sensitivity by changing the dilution ratio to as low as 5×. Published patent application US 20110092377, adopted these methods so that all of the processing of samples-producing mixed solutions, filtering and measuring them in well plates, etc. could be automated.
The references, Minogue et al 2005, Agrawal et al 2006, Ashley et al 2007, Agrawal et al 2008 and Agrawal et al 2011, verified the system developed in the above patents and applications by providing experimental evidence of practically using the method on surface wipes, air samples, soils and other bulk samples and reaching the desired detection limits.
The present invention is a technological change over both Matsumiya and U.S. Pat. No. 7,129,093. In the current invention a highly alkaline dye solutions is used as compared to both Matsumiya and U.S. Pat. No. 7,129,093. This change in the dye solution does not impact the procedures for sample preparation including the sample dissolution methods for refractory materials or automation disclosed in the other patents and patent applications discussed above.
All of the above methods (use of titration or use of buffered solutions) were based on an observation by Matsumiya that in order to determine beryllium quantitatively using fluorescence one has to be in a pH range of about 10 to about 12.85 (with a peak intensity at about 12.6 pH), and preferably between about 11 and 12.85. Since the measurement solutions comprised of a basic dye solution and a sample solution containing beryllium which was typically acidic for most situations, the dye solution started out with a pH of 12.6 to 12.85 and when mixed with the sample solution resulted in a desired pH to make the measurements. We made a surprising discovery, that one can quantitatively determine beryllium in a wide pH range and a suitable pH can be highly basic as compared to the prior art. One can start out with dye solutions with pH at or higher than 12.9 and even make measurements at pH higher than 12.9 (i.e., after mixing with the acidic solutions) with no loss in system performance or loss in the limit of detection of the beryllium amount, and as shown even getting better detection limits when one starts out with highly alkaline solutions.
The current invention of using highly alkaline solutions overcomes several disadvantages in the prior art methods, specifically, Matsumiya's method and the method taught in U.S. Pat. No. 7,129,093 and the U.S. Pat. No. 8,945,931. The prior art methods force the preparation of solutions so that the measurement solution pH (mixture of the sample and the dye solution) is in a narrow range. In addition, use of lysine as buffer in U.S. Pat. No. 7,129,093 is not convenient. Lysine is derived from natural sources, and has different impurities depending on the source and has to be purified to get consistent fluorescence background signal. Further many of the refractory materials or particles with larger sizes of refractory materials such as high fired beryllium oxide (e.g., see Goldcamp et al 2009), beryllium ores such as beryl and bertrandite, etc., require more acidic solutions to dissolve beryllium in a reasonable time (even if elevated temperatures are used, e.g., at or below 100 C or above 100 C in pressurized vessels). These concentrated acidic solutions when mixed with buffered solutions of U.S. Pat. No. 7,129,093 will result in a large pH drop which would then decrease the fluorescent signal. One could mix the concentrated acidic solutions with water or dilute acidic solutions after beryllium has been extracted before mixing them with the dye solution, however, this decreases the amount of beryllium in the sample solution and hence compromises the system detection limit. Even further, when metal alloys such as aluminum (or its alloys) need to be dissolved in acids to determine beryllium content, one tends to use stronger acids (e.g., use of HF rather than ammonium bifluoride (ABF) solutions), then it is difficult to maintain the pH of the mixture while also maintaining high sensitivity (or lower beryllium detection limit). U.S. Pat. No. 8,945,931 makes use of the dye solutions in U.S. Pat. No. 7,129,093 but lowers the dilution ratio from 20× down to 5× to increase the detection limit. In addition, a further increase in pH of the dye solution also causes other metals to precipitate faster (e.g. iron, titanium, etc.), and reduces their interference with beryllium measurement. These metals cause the solution color to be yellow which interferes with beryllium measurement. The fluorescent method typically measure beryllium in a wide dynamic range from about 20 μg down to the limit of quantification (limit of quantification (LOQ) is typically 3.33 times the limit of detection (LOD)).
This invention uses highly alkaline dye solutions to overcome the above disadvantages.
One objective of this invention is to use highly alkaline dye solutions (which may be either buffered or non-buffered), where these are mixed with the sample solutions containing beryllium so that beryllium can be quantitatively determined using fluorescence intensity which results from the interaction between the dye and beryllium and is proportional to the beryllium content.
Another objective is to be able to use higher acidity solutions to extract beryllium from more refractory solids which can then be used to mix with dye solutions so that beryllium can be quantitatively determined using fluorescence while also allowing one to maintain finer beryllium detection limits.
Yet another objective of this invention is to substitute the buffered dye solutions in standard test methods using optical fluorescence to detect beryllium such as ASTM D7202 and ASTM D7854 and other equivalent methods where the buffered dye solution with lower pH may be substituted by the higher pH dye solutions of this invention while keeping all of the advantages of these test methods and the present innovation.
In another objective, this invention provides a procedure to be able to use dilution ratios lower than 5× to increase the system sensitivity or detect smaller amounts of beryllium.